[ChiragM]

Thanks to Ghanshyam for sending this in. Heartfelt gratitude for sharing it with other enthusiasts via this Team-BHP page!

Hello, I am Vasanth.

I am a BHPian from the past 1 year or so.

We own a Mercedes CLA 200 CDI and it will turn 5 years old in 2 months. Well, the car has been mostly good. Its a very good highway cruiser, long-distance mile muncher, has a super silent cabin, etc. like all other Mercedes.

There is one part where it has been giving us problems. Believe it or not, in 5 years of our ownership, our car has been transported on a flatbed truck 4 times. And it is only due to the ABS sensor malfunction. No other reason. 2020 is the only year it has not happened. Well, ‘thanks’ to the pandemic. The car’s steering becomes very tight, and speed is restricted to 70 kmph. The brake pedal become very hard & tight. The car can be pulled over. Once it stops, sometimes the gearbox fails to shift to Drive mode. Eventually, it will work.

It has done 49,000 kms right now.

And yes. We have done a lot of trips. We have covered almost 800 - 900 kms one way, done in 16 -17 hours. Nowhere has it broken down. Touchwood. And almost every Saturday or Sunday, it does 220 kms.

When it happened for the third time, we asked the truck driver if he gets a lot of Mercedes’ to transport like this. He said yes. Not a lot, but not uncommon. And we asked - 'which model have you transported?' He said even the GLA.

It has been mixed feelings. We think it won’t happen again, but it does. The dealer fixes this problem in a day or two under warranty. I would like to know if all other Mercedes’ models suffer from the same problem time to time? Or is it only the base models?

This is an old picture taken in September of 2019. I don't have a better picture. Apologies for the clarity. It says ‘ABS and Traction control currently unavailable, Please see Owners manual’:

[GTO]

Not weird that the ABS sensor fails, as almost all German cars I know of - whether from VAG or Mercedes or BMW - suffer multiple ABS sensor failures over a 5 to 10 year ownership period. However, in all of these cases, it is a warning light on the instrument console, perhaps faulty ABS functionality (drive slowly) & a quick visit to the workshop.

What is weird is the car requiring a flatbed! Till date, I haven't heard of ABS sensors causing the car to become undriveable.

[androdev]

Your case seems to be too extreme. This problem starts off as an intermittent one - ABS error shows up on the instrument cluster and then switching off/on engine will make it go away and the car drives normally. The problem should be attended to immediately after reaching home, etc. If unattended, things escalate and this error will stay on permanently. Not having a working wheel speed sensor affects lot of control modules and it is not safe to drive if engine restart doesn't restore normal brakes/steering functionality. From what I know, there are enough "warnings" given to the driver before things get that far.

If my memory serves me right, I had this error come up once and went away when I restarted the car. I ignored it as I didn't know much about this error back then. I did remind the dealership during the service visit and they told me it's due to weak battery. Battery was indeed weak and due for replacement but I think it was not the correct diagnosis, they were just too lazy to do a preventive under-warranty repair. The error cam back again after a couple of months (battery was new) and went away when I restarted the car. I could drive down all the way from Pondicherry to Bangalore without any issues. They replaced both the front axle sensors under warranty and haven't seen this problem since then.

Wheel speed sensors fail due to collection of road dust, grime, brake metal dust, etc. This is not a fully enclosed system because it requires one part to be fixed on the rotating wheel and another to be fixed on the chassis to sense the wheel rotation. Depending on the design, location, number of sensors and more importantly driving conditions (dust, mud, heavy braking, brake pad material) these sensors will fail with varying frequency. I have a theory that these sensors are magnetic-field based and heavy braking + soft brake pad material used by the German brands hasten the failure.

Unfortunately I don't have any solution for your problem but some understanding of the problem might be helpful :-) I would try to find out the following:

1. Don't you get any warning signs before it requires to be taken on a flatbed?

2. Is it a case of each sensor taking turn to fail at different times? Or same sensor repeatedly failing? You can ask the dealer to show you the diagnostic scan report to verify the sensor location and fault description to confirm this. You said it has done 49K km - what is the mileage at the time of each failure?

3. How is your braking habit, how often do you change brake pads? Is there correlation between the brake pads you change and the location of faulty sensors?

4. Insist on seeing the ABS sensor diagnostic scan report each time you send the car for schedule service so that you can do some preventive maintenance if required. I don't know the cost of replacing sensors but now that you know the "service life" of these sensors going by the history of your car, you could attempt to replace them after certain mileage.

5. Not many drivers are mindful of how excessively they brake because they don't bother to anticipate the traffic. Most drivers of German cars love to hold good speeds - if you don't anticipate traffic, your car will be begging for some 'mechanical empathy' :-)



Note that both front sensors are replaced at once (I suspect one of them is preventive maintenance)

[Sanidhya mukund]

I think this is a very common problem on Mercedes cars. Even mine had this failure at the 4 year mark. When I saw the part that they had replaced, I was shocked to see that this wire like part with plastic ends costs 11K for one side!

Originally Posted by GTO

What is weird is the car requiring a flatbed! Till date, I haven't heard of ABS sensors causing the car to become undriveable.

When mine failed, I got the exact same warning on the instrument cluster as the one pictured above, but I did not experience any of the symptoms mentioned. Mine was perfectly drivable.

[Jeroen]

Sorry to hear about this ordeal. It is very relevant whether it was the same sensor (location) that broke four times, or multiple sensors from different wheels.

The traction control not being available is directly related to the ABS failure. But it should not prevent you from driving the car. Not sure why it had to go on the flat bed truck?

ABS sensors do fail now and then, but if it is a case of the failure on the same position (i.e. wheel) I would have some serious doubt to the level of workmanship in mounting new ones. I am not familiar with the exact procedure of swapping ABS sensors on a Mercedes. It often requires working according to a set procedure and using some special tools, including torque wrench.

An ABS sensor incorrectly installed, or if there is a problem with the position bracket is very likely to fail in due course. Chaffing and damage to the wire loom and connectors is another reason. Although a relative straight forward component, it does need proper care and due diligence when working on these.

If your problems were with four different sensors/locations I would suspect something else, more like the central control unit.(or wiring). As mentioned by other members, it is really important to get the full print out of the OBD scanner. Is it just the sensor, or are any other errors showing.

Good luck

Jeroen

[benu9714]

My experience with a Mercedes C200 (4 years) E240 (4 years) in the Middle East have been bad. Both cars were new and I was the only driver.

The C200 refused to start one morning. It was towed to the workshop and I was told that the fuel injection system had developed a fault and the entire assembly had to be replaced. The assembly came from Germany and it took 15 days. Meantime the workshop removed the F.E. unit from another (crashed) car and installed it in mine!

The E240 refused to start on a hot 48 degree afternoon in the middle of an open parking lot. It turned out that the ignition key was faulty and had to be replaced with a new unit which took 17 days. No cannibalised part available this time, unfortunately.

I was planning to leave the E240 in the Muscat airport parking lot to take a flight to Mumbai for an overnight trip, back the next evening. I rolled down the driver-side window at the parking lot gate, took the ticket and found that the window would not roll back up. After frantic "rescue" calls two drivers arrived from the office and took the car away.

I was told that the window drive mechanism used a rubber drive belt which deteriorated in heat and humidity and lost tension!!

I am reminded of an old saying "When she's good, she's very, very good. When she's bad, she's horrid."

[kamilharis]

Sorry to hear about the ordeal.

But I just think of this always - Why does a company like Merc or VAG that does the best of engineering in the automotive world fail in providing a better quality ABS Sensor or Injector? Why do their cars just come up with un-expected breakdowns every now and then?

[deepakc]

I own a BMW E90. I have faced this ABS sensor issue twice in a years time. Once the first one was replaced, within a few weeks I got the ABS sensor warning again. Turned out that the ABS sensor on the other front wheel was kaput. Both times I never had any issues with driving the car. As a quick fix for the warning light and chime I used to turn off the traction control till the sensor was replaced. So the fact that you need a flat bed as the car becomes undrivable seems to be a bigger issue than only the ABS sensor.

[androdev]

Just to give an idea of a dirty ABS sensor.

[Salnv]

Originally Posted by androdev

I ignored it as I didn't know much about this error back then. I did remind the dealership during the service visit and they told me it's due to weak battery. Battery was indeed weak and due for replacement but I think it was not the correct diagnosis

I think he may be right in this first level of investigation, but on top of that your would have had sensor issues too. I had similar issues in my ecosport and a good SA correctly found out that it was because of weak battery and was right. He told that you may get multiple warnings like ABS/Traction control unavailable/faulty etc primarily due to the unstable voltage supply to sensors, if not the fault with sensor itself, hence based on the model/make/manufacturer it may throw out different warnings related to sensors as the sensors would be malfunctioning due to voltage variations.

[Malluspec]

This is a common problem in the base generation of the Mercedes cars . GLA, CLA , A Class owners all have reported frequent abs failures especially in humid and water logging areas . In the present generation mercs as soon as abs fault comes the vehicle enters safe mode and hence undrivable . Very tight steering, transmission failure and jerky breaking. Flatbed is inevitable.

[Vasanth]

1. Don't you get any warning signs before it requires to be taken on a flatbed?

I forgot to mention
The car is driveable but with the following symptoms:
- Tight steering wheel
- Hard brake pedals
- speed limited to 70kmph
But the Mercedes service assistant requests us not to drive. The breakdowns were around 15-25 kms away from our home. We were able to drive back home safely but with the mentioned symptoms.

2. Is it a case of each sensor taking turn to fail at different times? Or same sensor repeatedly failing? You can ask the dealer to show you the diagnostic scan report to verify the sensor location and fault description to confirm this. You said it has done 49K km - what is the mileage at the time of each failure?

Will share the report and scan at a later date.
Yes the sensor fails once every year. But never twice in the same year. (Except in 2020. Probably because of pandemic and low mileage?)
With the fact that it has done almost 50k km in 5 years I assume that it fails once every 10k kms

3. How is your braking habit, how often do you change brake pads? Is there correlation between the brake pads you change and the location of faulty sensors?

On dual carriageways we travel at around 100-120kmph. There was a time when we used to brake the car late in case of a hump or speed breaker. (Not because we did not see the hump, it’s because the brakes are just so good)
The brake pads were replaced at around 38k kms in December 2019. (We got a message in the instrument cluster saying ‘Change brake pads’)
Is this too early ? Or could it be due to our driving style ? We do a long distance trip at least once or twice in a year. And they were always on expressways (Tamil Nadu, Karnataka , and Andhra)
In Kerala roads we have very much sedate driving style.

[Vasanth]

Originally Posted by Jeroen

Sorry to hear about this ordeal. It is very relevant whether it was the same sensor (location) that broke four times, or multiple sensors from different wheels.

The traction control not being available is directly related to the ABS failure. But it should not prevent you from driving the car. Not sure why it had to go on the flat bed truck?

ABS sensors do fail now and then, but if it is a case of the failure on the same position (i.e. wheel) I would have some serious doubt to the level of workmanship in mounting new ones. I am not familiar with the exact procedure of swapping ABS sensors on a Mercedes. It often requires working according to a set procedure and using some special tools, including torque wrench.

An ABS sensor incorrectly installed, or if there is a problem with the position bracket is very likely to fail in due course. Chaffing and damage to the wire loom and connectors is another reason. Although a relative straight forward component, it does need proper care and due diligence when working on these.

If your problems were with four different sensors/locations I would suspect something else, more like the central control unit.(or wiring). As mentioned by other members, it is really important to get the full print out of the OBD scanner. Is it just the sensor, or are any other errors showing.

Good luck

Jeroen

Apparently, the GLA and CLA are the most common in the Mercedes line up to be affected according to the driver who came to drop by our car.
He says it is because of coastal area. (So what about the other models?)
He also added that cars from this generation are affected by this. (2014-2016)
But not the new GLC, GLE, E class , S class etc. Supposedly the newer ones use different type of ABS system, programming , wiring harness etc. (words of the driver who came to drop our car)

Can we still trust the Mercedes brand ?
Must say there hasn’t been any other breakdowns on our car. And it sure is a joy to travel long distances

[mrBenz]

hey Vasanth, seems that you have two problems at once.

one is that the ABS sensors fail again and again which causes your vehicle to disable the ABS operations and give you the warning lights

seconds is that the ABS pump is forcing the car into limp mode by not allowing it to exceed 70kmph and or restricting shifting of gears.

I frankly think its more than just ABS sensors failing due to age or other issues. I think the ABS sensors (which are nothing but HALL Effect sensors) which were replaced arent the correct ones. As using incorrect ABS sensors will cause premature failure of both the Sensor itself and the ABS pump. I think this is what might be putting your vehicle into limp mode.

Granted the ABS pump hasnt showed signs of distress but there are a few ways to diagnose the situation better. The most easiest way is to use a XEntry scanner tool (ones used by Mercedes) to scan the sensor outputs when the vehicle rolls forward or backward. If your voltage values remain constant on all four wheels then your sensors are the correct type. If not you will see different values for different wheels and this confuses your ABS system as it has to work overtime to control the "false" slip which it detects due to improbable values.

These improbable values bring us to the second part of the issue with the ABS pump, if the values are improbable then the ABS pump is shut off to protect it from over working. which might put your vehicle into limp mode.

if your vehicle has always been serviced by the dealer then try to diagnose the issue with them by cross referencing the new replacement/updated parts available for the same part number. Weirdly mercedes sometimes does not issue a recall but instead just issues an updated part for the same old one as it would have failed many times in the past.

and if all above fails, then look at getting something done before the warranty expires as these things cost a hell of a lot once you need to replace them at your own expense.

Hope the above helps.

[AKSarkar1]

This is definitely a common hassle for all of us BHPians driving German cars in India. My daily driver (a VW) has had 5 ABS faults in 5 years, so almost at least one fault per year!

My last ABS fault however was the most annoying one, the car electrics went haywire and the SA blamed it on some fault in the system. I remember reading a similar experience of a fellow BHPian who got fed-up with ABS problems on his VW. After giving my VW workshop manager a piece of my mind, they quickly proceeded to rectify the fault under goodwill.